Japanese Patent Application Laid-Open Publication No. 2002-217495 (Patent Document 1) discloses technique of suppressing impurity diffusion to an active layer and also increasing characteristic temperature and modulation frequency for a semiconductor laser in which at least an n-type cladding layer, a bottom optical wave guiding layer, an active layer, a top optical guiding layer and a p-type cladding layer are stacked on a semiconductor substrate.
More specifically, by using Al0.5In0.5P which is lattice-matched to a gallium arsenide (GaAs) substrate and having the largest bandgap among AlGaInP-based semiconductors to the p-type cladding layer and the n-type cladding layer to obtain a bandgap difference between the active layer and the cladding layers, electron overflow from the active layer to the p-type cladding layer is suppressed. Also, diffusion of a dopant (zinc (Zn), selenium (Se)) doped to the p-type cladding layer and the n-type cladding layer at a high concentration, i.e., 1×1018 cm−3 into the active layer is suppressed by providing an undoped layer between the active layer and the p-type cladding layer and between the active layer and the n-type cladding layer, respectively.
Japanese Patent Application Laid-Open Publication No. 2006-120968 (Patent Document 2) discloses technique of improving efficiency and temperature characteristics of a semiconductor laser having an active layer between an n-type cladding layer and a p-type cladding layer. More specifically, according to Patent Document 2, generation of misfit dislocation is suppressed by forming the p-type cladding layer and the n-type cladding layer with lattice-aligned Al0.5In0.5P and introducing a strained layer for inhibiting overflow of electrons between the active layer and the p-type cladding layer as well as making the thickness of the strained layer smaller than or equal to a critical thickness.
Japanese Patent Application Laid-Open Publication No. 2011-023493 (Patent Document 3) discloses technique of reducing catastrophic optical damage (COD) at end facets and also improving stability of output beam for an AlGaInP-based semiconductor laser of a horizontal cavity type having a lasing wavelength shorter than 650 nm. More specifically, according to Patent Document 3, dissipation of an optical waveguide structure near end facets occurring when a window structure is formed by diffusion of an impurity such as Zn near end facets is suppressed by forming the optical waveguide layer excluding a well layer with (AlxGa1-x)InP where x>0.66. In addition, in the semiconductor laser, the n-type cladding layer and the p-type cladding layer are formed of Al0.51In0.49P or (Al0.9Ga0.1)0.51In0.49P.
Note that, a band gap of an AlGaInP-based semiconductor is 2.3 eV when x=0.7 in (AlxGa1-x)0.5In0.5P. However, it is reported that the bandgap is 2.35 eV when x=1 and it is the largest value among AlGaInP-based semiconductors (see D. P. Bour, R. S. Geels, D. W. Treat, T. L. Paoli, F. Ponce, R. L. Thornton, B. S. Krusor, R. D. Bringans, D. F. Welch (1994). “Strained GaxIn1-xP/(AlGa) 0.5In0.5P heterostructures and quantum-well laser diodes”, IEEE Journal of Quantum Electronics—IEEE J QUANTUM ELECTRON, vol. 30, no. 2, pp. 593-607 (Non-Patent Document 3)).